The walls of high-temperature gas reactors, such as gas turbine combustion chambers operating under pressure, must be protected from hot gas attack by means of suitable shielding for their supporting structure.
The heat shields comprise a supporting structure and heat shield elements which are arranged areally and are attached to the supporting structure, and which protect the supporting structure and the combustion chamber wall from hot gases. Ceramic materials are suitable for the material of the heat shield elements. In contrast to metallic materials, ceramic materials have high temperature resistance, corrosion resistance and low thermal conductivity. Also known, however, are metallic heat shield elements which are equipped with a thermal protection layer. Due to material-specific thermal expansion properties, and the temperature differences which typically arise in the context of operation (ambient temperature when stationary, maximum temperature at full load), temperature-dependent expansion of the heat shield elements must be guaranteed, in order to prevent thermal stresses—which could destroy the components—arising as a consequence of obstructed expansion. This can be achieved by lining the wall which is to be protected from hot gas attack with a multiplicity of small, individual heat shield elements. An expansion gap must be provided between the supporting structure and the individual heat shield elements; for safety reasons, this gap must never be entirely closed, even during operation. In that context, it must be ensured that the hot gas does not excessively heat the supporting wall structure via the expansion gap.
Due to the geometric shape of the known heat shield elements in the gas turbine combustion chambers, the uncovered surfaces of the supporting structure (the expansion gap) and projecting edges of the supporting structure are not optimally protected from the thermal load of the combustion chamber. As a result, at these points the supporting structure is subjected to thermal overload which must be repaired at great expense. What makes this more difficult is that the gaps which are required for thermal expansion cannot be optimally set because of the combustion chamber components which are subject to tolerances. The coarse tolerance zone of the components results in excessively large expansion gaps in the gas turbine combustion chamber. This makes it possible for the hot gas to penetrate into the expansion gaps and damage the metallic components. The damaged components must either be replaced, or it is possible to grind out the damaged areas of the supporting structure and subsequently carry out deposition welding and re-machining of the affected areas. It is also possible to coat the thermally loaded areas with a ceramic protective coating, or to deposit a high-temperature alloy onto components subject to high thermal load.